Poor attic ventilation can result in high air conditioning bills in the summer, excessive moisture retention in the winter, loss of insulation efficiency, and destruction of the roof sheathing. To eliminate these undesirable effects, adequate attic ventilation must be provided.
An attic ventilator designed for proper ventilation must effectively utilize the natural forces of temperature and wind. The temperature force, or commonly referred to as the thermal effect, results from a temperature differential between the attic enclosure and that of the outside, coupled with the difference in elevation between the highest and lowest ventilator openings. In order to minimize the thermal effect, a roof ventilator must provide maximum venting capacity, and be disposed at the highest possible elevation.
The force of wind, or commonly referred to as wind pressure, is created when the wind flows over a building, thus creating a vacuum therein. This vacuum produces a negative pressure area on the upwind side of the building and a positive pressure area on the downwind side of the building. Thus, ventilation air moves into the attic through openings in positive pressure areas and exhausts through openings in negative pressure areas. Because the ridge of the roof is always in a negative pressure area, a ventilator disposed on the roof ridge is an exhausting vent. Therefore, in order to minimize the effects of wind pressure, a roof ridge ventilator must provide maximum venting capacity to allow the exhausted attic air to exit therethrough without restriction and must present a low profile for allowing the wind to pass cleanly thereover.
An attic ventilator designed for proper ventilation must also be structurally impervious to foreseeable adverse conditions such as collapse from compressive loading and warpage from summer and winter temperature extremes.
More specifically, it is foreseeable that a person will step on the ventilator during its service life on the roof ridge. If the ventilator collapses under such a compressive loading, its ventilating capacity will be rendered either partially or totally impaired. Therefore, the ventilator must be designed to withstand all foreseeable loading conditions.
Additionally, it is foreseeable that temperature extremes will cause warpage. If the ventilator is fabricated from a thermoplastic material, such as polypropylene, then the possibility of warpage during the temperature extremes of summer will be readily appreciated. More specifically, should the warpage result in the ventilator's air flow passages separating or otherwise enlarging, then an entrance for small animals and the like into the attic is provided. Should the warpage result in the ventilator material softening and consequently creeping, then the air flow passages will contract and thereby diminish the flow capacity. Therefore, the ventilator must be designed to withstand all foreseeable temperature conditions.
Low profile ridge ventilators are known in the prior art. One example of this is shown in the U.S. Pat. No. 2,799,214 to Roose, issued July 16, 1957. The Roose ventilator has a generally inverted V-shaped cross section for conforming to the roof pitch and extends continuously along the roof ridge. An air passage is provided between vent inlet ports and vent outlet ports. The Roose ventilator is deficient in that no support is provided in the air passage between the inlet and outlet ports. That is, the air passage is completely open along the entire length of the ventilator. Accordingly, the vent structure is weak and capable of collapsing upon a sufficient compressive force thereby closing off the vent openings and severely restricting or cutting off the air flow therethrough.
Another example of a low profile roof ridge ventilator is disclosed in the U.S. Pat. No. 4,280,399 to Cunning, issued July 28, 1981. The Cunning ventilator comprises an elongated sheet having longitudinally extending corrugations therealong and vent slots disposed through the side walls of the corrugations. A cap shingle is disposed over the roof ridge ventilator for covering the otherwise exposed roof ridge opening. The Cunning ventilator is deficient in that the cap shingle covering the ventilator provides no support in the trough areas between adjacent corrugations. In other words, a compressive force, such as a person walking on the ventilator, would collapse the cap shingle into the trough portions between adjacent corrugations thereby restricting or cutting off the air flow therethrough. Additionally, the Cunning ventilator requires that the central portion thereof be nailed into a ridge beam extending continuously along the roof ridge. It will be readily appreciated that not every roof structure includes a ridge beam extending therealong.
Another example of a low profile roof ridge ventilator is shown in the U.S. Pat. No. 4,676,147 to Mankowski, issued June 30, 1987. The Mankowski ventilator comprises a one-piece cover member having a hinge extending centrally therealong and including two baffle sections disposed under the cover on opposite sides of the hinge. The baffle sections include a plurality of longitudinally spaced support walls extending approximately one half of the transverse length thereof. That is to say, the support walls do not have peripheries conforming to the entire cross sectional area of the baffle sections, therefore they are not capable of supporting the entire baffle sections under rather heavy compressive loading. A plurality of circular air inlet openings are provided in an inner wall of the baffle sections. The Mankowski ventilator is deficient in that the partitions neither rigidly nor unyieldingly support the baffle sections against the cover member. That is, because the support walls do not extend the entire transverse length of the baffle sections, the ventilator is collapsible in the unsupported areas. Additionally, the baffle sections are not securely fastened to the lower surface of the cover, thereby rendering the ventilator vulnerable to severe warpage during temperature extremes. Further, the design of the air inlet openings can not accommodate foreseeably high exhausted air flow rates while maintaining its low profile characteristics.